Sleeve for indirectly heated cathode



g- 1959 J. G. WOEHLlN ETAL 2,900,554

SLEEVE FOR INDIRECTLY HEATED CATHODE 1 Filed June 1. 1951 V Z12 Z5 I Gttorneg Patented Aug. 18, 1959 SLEEVE FOR CTLY HEATED CATHODE John George Woehling, Verona, and Robert Frie'dli, Jr., Short Hills, N..l., assignors to Radio (Importation of America, a corporation of Delaware Application June 1, 1951, Serial No. 229,466

7 Claims. (Cl. 313-337) The present invention relates to sleeves for indirectly heated cathodes and more particularly to a sleeve of relatively small diameter having an improved seam, and to a novel method of making such sleeve.

Cathode sleeves employed in standard size electron tubes have heretofore generally been made from elongated metal stock formed to tubular shape and With the longitudinal edges of the stock joined in a four thickness lock seam. The formed sleeve is therefore relatively thick at the region of the seam. To preserve a uniform outer contour of the sleeve to facilitate assembly thereof in an electrode cage, the thickened seam is usually disposed within the sleeve.

The thickness of the seam and the disposition thereof within the sleeve involves several serious difiiculties. These difi'iculties arise to a certain extent no matter What the size of the sleeve, but are particularly troublesome in connection with relatively small sleeves having a diameter of the order of 30 mils.

One of these difiiculties is presented as a consequence of reduction in the space Within the sleeve resulting from the accommodation of the thick seam therein. This reduction in space may seriously limit the type. and number of folds in a heater to be inserted in the sleeve. If a heater structure is larger transversely than a crosssection of the space within the sleeve, it is obvious that it cannot be received Within the sleeve. But even though the heater structure can be accommodated Within the sleeve, the reduction in the space therein by the seam seniously affects the operation of extending the heater into the sleeve.

In addition to the foregoing difficulty, the relatively massive lock seam of the prior art has adversely affected electron emission from a cathode in which the sleeve is used. For example, the lock seam has prevented a uniforming heating of the sleeve due to the thermal inertia of the concentrated sleeve material at the lock seam.

In sleeves of relatively small size, such as of the order,

of 30 mils diameter or smaller, the difiiculties mentioned above have rendered it entirely impracticable to use a lock seam. As an alternative to lock seams in these small sized sleeves, it has been proposed to form the sleeve With the longitudinal edges thereof in abutment and rely on the "s'tifiness of the sleeve material for holding the edges together. However, this was discarded because no way could be found to insure that no gaps or small openings occurred along the joint. Such gaps or small openings would adversely affect the performance of an electron tube in which the sleeve were used, as a result of heater to cathode leakage.

lems in spraying the sleeve with emitting material. Furthermore, sleeves heretofore having a joint formed by V overlapping portions, lack desired circular shape in crosssection.

As a consequence of the foregoing difficulties in connection with lock seamed sleeves and the absence of suitable alternatives, it has been necessary heretofore to resort to seamless tubing for providing cathode sleeves of relatively small size as aforementioned. However, while seamless sleeves made from seamless tubing are very well suited for use in small sized cathodes, they are objectionable for several reasons. From the standpoint of cost, flat sheet metal stock from which seamed sleeves can be fabricated, is appreciably cheaper than seamless tubing from which seamless sleeves are made. Furthermore, it is difficult, if not impossible, to provide cathode sleeves with integral tabs from seamless tubing. Integral tabs on cathode sleeves serving as connectors to lead-ins, are desirable, since they render unnecessary the step of welding tabs to the sleeves. Another objection to sleeves made from seamless tubing is the fact that such tubing has surface contaminants from the forming operation and cannot be cleaned as well as sleeves made from flat strip. In the latter case, the cleaning operation can advantageously be performed prior to forming the sleeve and While the material is flat.

Accordingly, it is an object of the invention to provide a cathode sleeve of reduced cost.

A further object is. to provide a seamed sleeve suitable a seam of reduced thickness for preserving the uniformity of the inner and outer Walls of the sleeve.

Another object is to provide a cathode sleevehaving a seam formed by swaging two overlapping edge portions of a Work piece to form a strong joint between the portions.

A further object is to provide a swaged cathode sleeve wherein strains arising during forming are effectively released.

Another object is to provide a round cathode sleeve having two overlapping portions to form ajoint,

Another object is to provide an improved method of making a seam type sleeve.

According to one aspect of the invention, a swaged cathode sleeve is provided having-a joint formed by two overlapping portions of the sleeve material, and an integral tab. The swaging of the sleeve is effected at rela- 'tively high pressures so that strains set up in the material during the forming thereof to sleeve shape, are released, so that once the sleeve is formed, the natural stiffness of the material contributes to a retention of the sleeve shape.

According to another aspect of the invention the overlapping portions of' the sleeve forming the joint are bent to a degree beyond their elastic limit so that the engagement 'between the portions referredis set to thereby prevent an opening at the joint.

A further aspect of the invention involves a swaged engagement between the overlapping portions of the sleeve to contribute to the strength of the joint therebetween and to supplement the natural stiffness of the sleeve material in holding the sleeve to desired shape. Furthermore, the swaged engagement between the overlapping portions, according to the invention, preserves the desired circular shape of the sleeve in cross-section.

The improved method of the invention utilizes a man drel having a generally round shape in cross section but having a flattened side. According to the methodof the invention, flat sheet stock having an integral tab is wrapped around the rounded portion of the mandrel with appreciable pressure, to substantially U shape. The pressure used is sufficient to release all strains in the material including strains produced by the elasticity of the sleeve material. The legs of the U-shaped form are then successively bent sharply around the two relatively sharp ridges formed on the mandrel at the junction of the flattened and rounded portions thereof. The sharpness of the resultant bend causes a deformation of the material be yond its elastic limit. The bent legs are then forced against the flattened portion of the mandrel with appreciable pressure, to further release strains therein. Thereafter, the sleeve while still on the mandrel is swaged to provide a round outer surface throughout, including the outer surface at the joint formed by the overlapping portions, to further release strains in the formed sleeve and to contribute added strength to the joint.

The novel sleeve of the invention is particularly advantageous when of relatively small size, such as about 30 mils in diameter. In this small size of sleeve, the

material of the sleeve is relatively stiff, so that the sleeve form is characterized by increased resistance to deformation as by opening up at the joint.

While the sleeve of the invention relies on the natural stiffness of strain-free material to reduce incidents of openings at the joint or seam, such openings are further prevented by the disposition of the overlapping portions at the seam in substantially parallel planes. Therefore, if some movement of one of the overlapping portions occurs in one of these planes, it will not provide an opening in the seam through which objectionable heater to cathode leakage can occur.

A better understanding of the invention will be had from a consideration of an embodiment thereof, by way of example, taken in connection with the appended dra ing in which Figure 1 is a side view of a cathode sleeve according to the invention;

Figure 2 is a sectional view along the line 2-2 Figure 1;

Figure 3 is a plan view of a work piece from which the sleeve of the invention is made; a

Figure 4 is a sectional elevation showing means used during the first step in forming the sleeve of the invention;

Figures 5, 6, 7, 8 and 9 show sectional elevations of means used in the several steps of wrapping the sleeve stock around a mandrel, during a practice of the method of the invention; and

Figure 10 'is a sectional elevation of means used in swaging together the overlapping edge portions of the sleeve stock, to form a strong joint of reduced stock material, and to complete the fabrication of the improved sleeve.

Referring now to the drawing in more detail, there is shown in Figures 1 and 2 a sleeve 10 for an indirectly heated cathode according to the invention. The sleeve includes an integral tab 11 for connecting the sleeve when incorporated in a cathode to a suitable lead-in conductor. The sleeve may also include an annular embossment 12 for suitably fixing the sleeve in an electron tube assembly.

According to the invention, the sleeve 10 has a seam or joint 13. The seam includes overlapping portions 14, 15, which effectively form a joint having several advantages. The joint referred to includes only two thicknesses of the material of the sleeve. Therefore, the joint is characterized by reduced thermal inertia. Furthermore, the reduced mass of the joint makes less demand on the space within the sleeve. Consequently such space is better adapted to accommodate a heater structure, such 'as a folded or coiled heater, not shown, and the step of inserting the heater in the sleeve is facilitated. It will be noted that the inner portion 14 has a substantially flat inner surface. While the outer portion 15 mount is rounded, the flattening of the inner portion serves to parallel planes. It will also be noted that in forming the sleeve, as will be apparent in the following, the end portions 14, 15 are subjected to relatively sharp bends which are appreciably beyond the limit of elasticity of the material of the sleeve. Therefore, should any relative movement occur between the overlapping portions referred to, it will be restricted to the two parallel planes referred to. 7 Such relative movement is effectively restrained according to the invention so that it can never involve a gap at the joint through which heater to cathode leakage can occur, or through which coating material might be inadvertently applied to the inner surface of the sleeve. The following features of the sleeve serve to restrain relative movement between the overlapping portions 14, 15 or at least to so limit any relative movement as to render it free from objection.

One of the features of the sleeve that contributes to strength of the joint 13 is the fact that the material of the sleeve is substantially free from strains that might tend to separation of the overlapping portions 14, 15. This characteristic is conferred on the sleeve by the novel method of its preparation to be described below. Thus, the sleeve is subjected to appreciable pressure as by swaging in manufacture and after it is formed, so that strains produced by forming it to round shape from-a flat state, are effectively released. Therefore, portions of the sleeve spaced from the joint 13 have ,no tendency to deviate from their rounded form and thus support the portions 14, 15 in overlapped relation.

Another feature that contributes to the strength of the joint 13 results from the step of the method of the invention that involves swaging or pressing the overlapping portions under appreciable pressure between a flattened side of a mandrel to be described and the concave surface of a swaging die, also to be described. As will be noted in Figure 2, the pressure so applied to the overlapping portions 14, 15, results in entrance of the relatively sharp corners 16, 16a formed by the junctions of the edges 17, 17a and the sides of the material of the sleeve. The pressure referred to also causes some of the material of portion 14 to flow to at least partly fill the groove formed by edge 17 and the outer surface of the sleeve to thereby not only strengthen the joint but also improve the uniformity of the outer surface of the sleeve. A similar flow of material occurs to at least partly fill the groove formed by the edge 17a and the inner surface of the sleeve, for increased joint strength and also for increased inner surface uniformity of the sleeve. In addition to the foregoing effect, it is also believed that a partial interdiifusion between the materials of the overlapping portions 14, 15 occurs. Although this interdifl nsion is probably very slight, it contributes to the strength with which the portions 14, 15 engage each other to eifectively prevent impairment of the joint therebetween.

Since the relative stiffness of the material of the sleeve increases with reduction in diameter thereof, the features aforementioned contributing to strength of the seam or joint of the sleeve according to the invention, are particularly advantageous in relatively small sized sleeves, such as of the order of 25 or 30 mils. The advantages of heater accommodation and heater insertion are also of increased importance in cathodes having the diameters referred to.

Referring now to the method of the invention, the novel sleeve of the invention is formed from a work piece shown in Figure 3 made of planar sheet metal. The work piece includes a body portion 18, an integral tongue 19 and an embossment 20 extending partly across the body portion 18.

According to the novel method of the invention, the work piece referred to is disposed between two forming members 21, 22 shown in Figure 4 having mutually curved surfaces 23, 24. The members 21, 22 are movable to vary the spacing between the surfaces 23, 24 thereof. When the'members 21, 22 are separated as shown in Figure 4, the blank shown in Figure 3 is placed therebetween as shown in phantom. Thereafter, the upper member 21 is moved downwardly towards the lower member 22 to apply an appreciable swaging pressure to blank 18. As a result of this pressure, the blank 18 is bent as shown in cross-section and strains therein caused by the bending thereof are released.

After the blank 18 is bent as shown in Figure 4, it is transported to a holding means comprising mandrel 25 and holding members 26, 27 as shown in Figure 5. Holding members 26, 27 hold the blank in position on mandrel 25 until forming member 28 and anvil 29 shown in Figure 6 engage the blank 18 and mandrel 25, respectively. The anvil 29 moves upwardly to engage a fiattened portion 30 on the mandrel 25 and to provide a support or anvil for opposing the force of the downwardly moving forming member 28 on the blank 18 and the mandrel. The forming member 28 has an elongated groove for receiving the mandrel 25 and the blank 18. The base of the groove has a curvature similar to the curvature of the mandrel. Thus, when the mandrel and blank referred to are received under appreciable pressure in the groove in forming member 28, the blank is caused to follow the curvature of the mandrel and to be partly wrapped around it. The pressure referred to is not only adequate to form the blank as shown, but to release strains set up therein during the forming operation. a

While the blank 18 continues to be urged partly around the mandrel 25 by forming member 28, the anvil 29 is lowered and a slide plate 31 shown in Figure 7 is caused to move to the right to bend a leg 14 of the U- shaped structure formed by member 28, against the flattened portion Stl of the mandrel, to further wrap the blank 18 around the mandrel. This bending of the leg 14 is of a magnitude beyond the elastic limit of the material of the leg.

Thereafter, slide 31 is moved to the left to disengage the blank and anvil 29 is raised, as shown in Figure 8, to swage or force the leg 14 firmly against the flattened portion of the mandrel.

The anvil 29 is then lowered again, and a slide 32 is caused to move to the left as shown in Figure 9, to bend the other leg 15 of the U-shaped form of the blank in Figure 6 in overlapping fashion over the leg 14- and beyond the elastic limit of the material of the leg. In Figure 9, the legs 14-, 15 become the overlapping portions 14, 15 shown in Figure 2.

It will be noted that during the four forming operations depicted in Figures 6, 7, 8 and 9, the forming member 28 continues to engage theblank 18 for applying a continuing pressure thereto and for preventing relative movement between the blank and mandrel.

After the forming operation shown in Figure 9 is completed, the former 28 is raised and the slide 32 is moved to the right so that the mandrel 25 and the blank 18 now completely wrapped around the mandrel, are free for action thereon by a swaging unit shown in Figure 10. This swaging unit comprises vertically movable swaging member 33 and anvil 34. The swaging member is provided with a rounded groove for partly receiving the mandrel 25 and the blank wrapped therearound. The anvil 34 is also provided with a groove having a rounded bottom for receiving the overlapping portions 14, 15 of the blank. The curvatures of the rounded groove in the swaging member 33 and the rounded bottom of the groove in anvil 34 complement each other to form a cylindrical space having a diameter equal to the outer diameter of the finished sleeve 10. To assure accurate registry between the grooves in swager 33 and anvil 34, the sides of the groove in the anvil are flared and the sides of the swager are tapered for snug receipt by the flared sides of the anvil groove.

After the mandrel 25 and the sleeve 18 wrapped therearound are received in the groove in anvil 34, the swaging member 33 is forced downwardly on the blank18 and mandrel 25, with suflicient force to cause the material of the overlapping portions 14, 15 to become deformed as mentioned above to provide a sleeve having a round outer surface and a strong two ply joint.

It will be apparent from the foregoing that an improved sleeve for an indirectly heated cathode is provided. The sleeve of the invention is believed to constitute the only practical alternative to a small sized seamless sleeve made from seamless tubing, and in fact is superior in respect of cost, washability, and feasibility of an integral tab. While the sleeve of the invention is of the seamed type, the seam is of reduced mass without sacrificing strength of the seam or its ability to provide an effective side closure for the sleeve to prevent objectionable exterior communication to a heater used in the sleeve.

What is claimed is:

1. A sleeve for an indirectly heated cathode, said sleeve having a relatively small diameter of the order of from 25 to 30 mils and including a seam extending longitudinally thereof and following the transverse contour of said sleeve, said seam comprising two overlapping portions only of the material of said sleeve, one of said overlapping portions having a relatively sharp edge extending into the material of the other of said portions to improve the uniformity in the outer and inner surfaces of said sleeve, and to increase the strength of said seam, the material of said sleeve comprising sheet metal, said sheet metal being relatively stiff when formed into a sleeve of said relatively small diameter, whereby said stiffness and said relatively sharp edge preserve said seam from opening.

2. A sleeve for an indirectly heated cathode comprising a rolled sheet metal structure having a seam extending longitudinally thereof, said sleeve having a relatively small diameter of the order of from 25 to 30 mils, said sheet metal being relatively stiff when formed to a sleeve of said relatively small diameter, said seam including two thicknesses only of said material in overlapping rela tion and following the contour of said structure, said material having a relatively sharp edge in one of said two thicknesses thereof, said edge partly penetrating the other of said two thicknesses of material, whereby openings in said seam are prevented.

3. A sleeve for an indirectly heated cathode having a seam extending longitudinally thereof, said sleeve having a relatively small diameter of the order of from 25 to 30 mils, said material comprising sheet metal that is relatively stiif in the form of a sleeve of said relatively small diameter, said seam. comprising two overlapping portions of the material of said sleeve following the transverse contour of the sleeve, one of said portions having a relatively sharp bend therein beyond the elastic limit of said material and having a relatively sharp edge, said edge being embedded in the other of said portions, whereby said seam remains closed.

4. A sleeve for an indirectly heated cathode having a seam formed by an inner and outer overlapping portion only of the material of said sleeve, said sleeve having a relatively small diameter of the order of from 25 to 30 mils, said material being relatively stiff in the form of a sleeve having said relatively small diameter, said inner overlapping portion terminating in an edge, said edge and a side of the material of said sleeve forming a relatively sharp knife edge, said inner overlapping portion being flat, the outer of said portions being rounded, said knife edge being at least partly embedded in the material of the outer of said portions, said embedment of said knife edge and the stillness of said material providing a seam of increased strength for advantageous use of said sleeve in a cathode.

5. Method of making a sleeve of curved cross-section for an indirectly heated cathode from elongated flat metal stock that is relatively stiff when formed to sleeve 7 shape having a relatively small diameter of the order from 25 to 30 mils, comprising the steps of shaping said stock under appreciable pressure to an intermediate form to reduce strains in said stock, shaping a portion of said stock intermediate the longitudinal margins thereof to the curvature of a sleeve having said relatively small diameter and under appreciable pressure to further reduce strains therein, bending one longitudinal margin portion of the stock towards the center of said curvature and beyond the elastic limit of said stock while preserving the flat character of said marginal portion, compressing said marginal portion to release strains therein, thereafter bending the other longitudinal edge portion in overlapping relation on said one longitudinal marginal portion to provide a double thickness seam, and compressing said seam to further release strains therein and to cause said marginal portions to become partly embedded in each other and to provide a curvature in the seam for rendering the outer surface of the sleeve substantially uniform, whereby the material of said sleeve is set against deformation and said seam is resistant to opening.

6. A cathode sleeve having a round outer surface and an inner wall defining a space'for receiving a heating element, said sleeve having a diameter of the order of from 25 to 30 mils, said sleeve being made of a metalthat is relatively stifi in the form of a sleeve of said diameter, said sleeve including a longitudinally extending seam formed of a first ply and a second ply only, to facilitate uniform heating of said sleeve by said heating element, said first ply being fiat and extending uniformly along said sleeve for facilitating extension of said heating element into said space, said second ply being rounded and forming a part of said round outer surface of the sleeve for facilitating mounting said sleeve in an electron tube, said first ply having a relatively sharp knife edge em- 8 bedded in said second ply, said second ply having a relatively sharp knife edge embedded in said first ply, whereby said seam is effectively locked against opening by the stiffness of said metal and the embodiment of said knife edge in said second ply.

7. A cathode sleeve having a seam extending longitudinally thereof, said sleeve having a diameter of the order of from 25 to 30 mils, the material of said sleeve being relatively stiff in the form of a sleeve of said diameter, said seam comprising only a first ply and a second ply, said first ply being flat and second ply being rounded, said first ply being disposed inwardly of said sleeve and extending across a segment defined by said second ply, said plies haying surfaces in contacting relation, said surfaces terminating in relatively sharp edges, said edges being embedded in said surfaces for locking together said plies, the embedment of said edges in said surfaces and the stiffnessof said material restraining said seam against openmg.

iReferences Cited in the file of this patent UNITED STATES PATENTS 440,512 Serve Nov. 11, 1890 694,994 Rowland Mar. 11, 1902 1,190,351 Wilsie July 11, 1916 1 1,895,133 Quarnstrom Jan. 24, 1933 2,075,910 Robinson Apr. 6, 1937 2,096,044 Johns Oct. 19, 1937 2,116,971 Haslauer May 10, 1938 2,118,765 Miller May 24, 1938 2,220,909 Kershaw Nov. 12, 1940 2,612,619 Friedli Sept. 30, 1952 t I FOREIGN PATENTS 75,038 Germany May 8, 1894 

